Share the wealth with your lawn. Leaves contain some of the nutrients that trees and shrubs have taken out of the soil, and it’s in keeping with nature’s plan that you should give back some of those purloined nutrients by mowing over part of your annual leaf-fall, thus returning organic matter to the soil from whence it came. This works best in early fall when the first leaves are coming down and grass still benefits from mowing. In addition to helping the lawn, it’s easier to rake turf areas that have been smoothed over by a good mowing.